Respective methods and detectors are known in the prior art. A scintillator in a scintillation detector absorbs the radiation to be measured, thereby generating excited states within the scintillator. Those excited states decay with a decay time τ under the emission of light, whereas the amount of light is a measure for the absorbed energy of the incoming radiation. The light is directed to a photocathode, emitting electrons in dependence of the amount of light, being absorbed there, being usually amplified by photomultiplier. The output signal of the photomultiplier therefore is a measure for the total energy of the absorbed radiation.
It is known that the light output of a scintillator is dependent from its temperature, so that the output signal, being proportional to the measured energy, is also dependent from the temperature of the scintillator. As it is often not possible to operate the scintillation detector at a constant known temperature, the detector's accuracy of measurement is substantially impaired by the temperature changes.
According to the known prior art, this is achieved by a calibration, being applied before or after the measurement, whereas a so called calibration source, that is a radiation source with a known energy of radiation, is used for calibration. As an alternative or in addition, the calibration may be effected on the basis of known lines with known energy, being present in the measured spectrum.
This has the disadvantage that temperature changes occurring between the time of calibration and the time of measurement, lead to an additional uncertainty of the measurement. Especially with detectors, being used under changing external operation conditions, especially outside of a laboratory, this disadvantage is of importance. Furthermore, it has often to be assumed, especially in security engineering—contrary to classical research applications—that they are not enough lines of previously known energy present within the spectrum, so that the measured spectrum has to be evaluated in advance in order to be able to allocate specific energies to single measured lines. Because of possible incorrect allocations, this is subject to errors As the security personal usually has no nuclear physics knowledge, the allocation of single lines of the measured spectrum to specific known energies is a difficulty in addition.